Determination of wheel sensor position using a single radio frequency detector in an automotive remote tire monitor system

ABSTRACT

A tire monitor system employs a single RF detector mounted on the vehicle. The tire monitor system also includes a control unit and a receiver. The single RF detector is positioned to be proximate a front axle or a rear axle. The RF detector also may be positioned off-center. The control unit distinguishes front tire monitors from rear tire monitors by comparing a number of RF transmissions received by each tire monitor. The control unit also may distinguish between left tire monitors and right tire monitors by comparing the number of RF transmissions received by each tire monitor. In other embodiment, the tire monitor system may further use a received signal strength and/or acceleration signals to determine position information of the tire monitors.

PRIORITY CLAIM

This application is a continuation-in-part of application Ser. No.11/030,837 filed Jan. 7, 2005, which is a continuation of applicationSer. No. 10/021,284 filed Oct. 29, 2001, each of which is incorporatedherein in its entirety by this reference. This application also relatesto application Ser. No. 10/125,043 filed Apr. 18, 2002 in the names ofWilliam David Stewart, Idir Boudaoud and Thomas David Stephen McClellandand commonly assigned to the owner of the present application, which isincorporated herein in its entirety by this reference.

BACKGROUND

1. Technical Field

The invention relates generally to a remote tire monitoring system. Moreparticularly, the invention relates to a method and apparatus fordetermining wheel sensor position using a single radio frequencydetector.

2. Background Information

Systems have been developed to monitor a characteristic such as tirepressure of a vehicle and to report the characteristic to a receiver ata central monitoring station using radio transmissions. A monitor islocated at each tire and periodically takes a measurement of the tirecharacteristic. The monitor then transmits the results of themeasurement in a radio frequency transmission to the central monitoringstation which produces an alarm or a display in response to themeasurement.

One problem with such systems has been the need to program the locationof the transmitters at the central station. To be fully useful, the tirecharacteristic data is preferably associated with the tire whichoriginated the measurement when presenting a display or alarm. Eachmonitor includes identification information which can be transmittedwith the measurement. The tire monitor is preferably activated toproduce this information and the information is then conveyed to thecentral station and associated with the position of the tire.

In the technique of U.S. Pat. No. 5,600,301, the tire monitors eachinclude a reed switch or other magnetic device. A magnet is passed nearthe reed switch, causing the monitor to transmit a radio frequencytransmission that includes identification data. A service technicianrepeats this process at each wheel and then loads the identification andposition information into the central monitoring station. Another methodprovides a printed bar code on each tire monitor which contains theidentification information and which may be read with a suitable barcode reader.

In U.S. Pat. No. 5,880,363, an activation signal is provided from thecentral controller to a low frequency transmitter at each wheel well.The transmitter generates a low frequency signal to activate the tiremonitor. The tire pressure monitor responds by generating a long waveidentification signal and transmitting that signal with tire pressureand identification data directly to the control unit. The long waveidentification signal is used to identify the position of the tire bydistinguishing this transmission from other transmissions received bythe controller.

U.S. Pat. No. 5,883,305 discloses two-way communication of data by radiosignals. A tire pressure monitor is activated by a radio frequencysignal transmitted by an antenna in the wheel well adjacent the tire.The tire pressure monitor transmits a second radio frequency signalwhich is detected by the wheel well antenna. The second signal isdemodulated to detect that tire pressure data.

These previous techniques have been limited in effectiveness. Themagnetic programming technique may be subject to interference andcrosstalk, for example in a factory where many such tire monitors arebeing assembled with tires and vehicles. The bar code label systemrequires a label at each tire which can be lost or become dirty orillegible. The apparatus for transmitting a long wave activation signaland generating a long wave identification signal therefrom is tooexpensive for some applications. The two-way data communicationtechniques require demodulation of the received radio signals at thewheel well and coaxial cabling back to the central controller, both ofwhich add to the cost of the system.

A further limitation of some of these prior techniques is the manualoperation requiring activation by a service technician. A system isdesired which automatically conveys wheel position data to the receiver.Such a system would be particularly useful after any change in tireposition, such as tire rotation or replacement of a tire.

U.S. Pat. No. 6,518,876, commonly assigned with the present application,discloses a system and method in which tire monitors are located at eachwheel of the vehicle and periodically transmit tire data along with atire monitor identifier. Four small, inexpensive RF detectors arelocated near each wheel. Each RF detector is connected to the centralcontrol unit by a power line and a ground line. When a tire monitortransmits data by emitting an RF transmission, the RF detector that isclosest to the transmitter will detect the burst of RF energy. The RFdetector responds to the RF energy by modulating the power line to thecontrol unit with the envelope of the transmitted data. The control unitdetects this modulation on one of its power lines. Also, the RF receiverof the control unit receives and demodulates the data transmitted by thetire monitor. The control unit associates the received data with theposition indication provided by the modulation on the power line. Whenthe positions of the wheels on the vehicle are changed, the control unitcan determine the new position using the modulated power line inassociation with the tire monitor identifier in the transmitted data.

While this system has been very successful in application, a systemfeaturing reduced cost and weight is desired. The cables that must berun from the control unit to all four RF detectors add substantially tothe cost and weight of an installation. Accordingly, there is a need fora system and method which provide the operational advantages of theearlier system in a system offering reduced complexity, parts count,weight and cost.

BRIEF SUMMARY

By way of introduction only, a tire monitor for use in conjunction witha remote tire monitoring system of a vehicle includes in one embodimenta single radio frequency (RF) detector, a receiver and a control unit.The RF detector is associated with a plurality of tire monitors todetect RF transmissions. Upon detection, the RF detector generates atransmission indication. Apart from the RF detector, the receiver isoperable to receive tire information from the plurality of tiremonitors. The control unit is coupled with the RF detector and thereceiver and operates to determine position of the plurality of tiremonitors.

In other embodiment, a remote tire monitor system for use with a vehiclehaving a front side, a rear side, a left side and a right side includesa single detector, a receiver and a control unit. The single detector isconfigured to position proximate one side of the vehicle. The singledetector generates a transmission indication in response to RFtransmissions from at least one of the plurality of tire monitors. Thereceiver is operable to receive the tire information and the controlunit is coupled with the single detector and the receiver. The controlunit is operable to determine a position of the plurality of tiremonitors based on the detected transmission indications and the tireinformation.

In another embodiment, a tire monitor method for a tire monitorpositioned at a wheel of a vehicle includes detecting RF transmissionsfrom a plurality of tire monitors and receiving tire data from theplurality of tire monitors. The tire monitor method further includesdetermining positions of the plurality of tire monitors based on thedetected RF transmissions and the tire data.

The foregoing discussion of the preferred embodiments has been providedonly by way of introduction. Nothing in this section should be taken asa limitation on the following claims, which define the scope of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of one embodiment of a remote tire monitorsystem shown in conjunction with portions of a vehicle;

FIG. 2 is a flow diagram illustrating one embodiment of an auto learnmethod for the remote tire monitor system of FIG. 1;

FIG. 3 is a flow diagram illustrating one embodiment of an auto learnmethod for the remote tire monitor system of FIG. 1;

FIG. 4 is a block diagram of a vehicle with a remote tire monitor systemusing two RF (Radio Frequency) detectors;

FIGS. 5 and 6 and are a flow diagram illustrating one embodiment of aremote tire monitor system;

FIG. 7 is a block diagram of a vehicle with a remote tire monitor systemusing a single front RF detector;

FIG. 8 is a flowchart illustrating a first example operation of theremote tire monitor system using the front RF detector;

FIG. 9 is a flowchart illustrating a second example operation of theremote tire monitor system using the front RF detector; and

FIG. 10 is a flowchart illustrating a third example operation of theremote tire monitor system using the front RF detector.

DETAILED DESCRIPTION OF THE DRAWINGS AND THE PRESENTLY PREFERREDEMBODIMENTS

Referring now to the drawing, it is a block diagram of a remote tiremonitor system 100 shown in conjunction with portions of a vehicle 102.The vehicle 102 includes in this example four tires 104. Other numbersof tires may be included, such as a fifth tire as spare or additionaltires if the vehicle is a truck, trailer or other multi-wheeled vehicle.

Associated with each of the tires 104 is a transmitter or tire monitor106. Each of the tire monitors 106 includes a battery powered, radiofrequency (RF) transmitter. Any suitable tire monitor may be used. U.S.patent application Ser. No. 09/245,938, entitled “Method And ApparatusFor A Remote Tire Pressure Monitor System,” filed Feb. 5, 1999 in thename of McClelland et al., and commonly assigned with the presentapplication is incorporated herein by reference and illustrates onesuitable tire monitor for use in the remote tire pressure monitor system100. Each tire monitor 106 includes a sensor such as a pressure sensorfor measuring a tire characteristic. The tire monitor 106 converts themeasured tire characteristic to tire data. The tire data is encoded fortransmission from the tire monitor 106.

The tire monitor further includes a transmitter configured to transmitRF signals including the tire data. In some embodiments, thetransmissions are encoded or randomized to minimize clashes at areceiver. For example, U.S. patent application Ser. No. 09/245,577,entitled “Method For Communicating Data In A Remote Tire PressureMonitoring System,” filed Feb. 5, 1999 in the name of Bailie, et al.,and commonly assigned with the present application is incorporatedherein by reference. This application shows a technique in which datawords are transmitted separated by a time delay. The time delay for eachrespective data word is defined according to a repeating pattern commonto the tires so that data words are transmitted during a plurality ofaperiodic time windows. Transmission parameters such as modulationtechniques, transmission frequency and transmission power are chosenaccording to local regulations and to assure reliable reception of theRF signals.

The tire monitor 106 includes a motion switch 139. The motion switch 139closes upon detection of movement of the vehicle 100. The motion switch139 provides a signal to the processor 124 indicating closure of theswitch 139 and motion of the vehicle. In response to closure of theswitch, the tire monitor system 100 begins operating, for example, bytransmitting tire data. In the illustrated embodiment, during normaloperation, the tire monitor 106 transmits supervisory tire pressureinformation once every minute. Any suitable motion switch may be usedfor the switch 139.

The remote tire monitor system 100 includes a control unit 110 and aplurality of radio frequency (RF) detectors 112. In alternativeembodiment, the remote tire monitor system 100 additionally includes auser display for providing user information such as tire pressureinformation and low tire pressure alarms. In the illustrated embodiment,each RF detector 112 is mounted on the vehicle 102 proximate anassociated tire monitor 106 to detect the RF signals from the associatedtire monitor 106 and produce a transmission indication in response todetected RF signals. Each of the RF detectors 112 is electricallycoupled by a conductor 114 to the control unit 110. Structure andoperation of the RF detectors 112 will be described in greater detailbelow.

The control unit 110 includes an RF receiver 120, an RF decoder 122, anda controller 124. The RF receiver 120 is configured to receive RFsignals conveying tire data from at least one transmitting tire monitor106 of the plurality of tire monitors 106 associated with the wheels ortires 104 of the vehicle 102. Any suitable RF receiver circuit may beused. The design and implementation of the RF receiver 120 will dependon the type of modulation used for the RF signals, transmissionfrequency for the RF signals, and physical limitations such as permittedsize, weight and power dissipation.

The RF decoder 122 is configured to receive a transmission indicationfrom at least one receiving RF detector 112 of a plurality of RFdetectors 112 associated with wheels or tires 104 of the vehicle 102.Thus, a tire monitor 106 will transmit RF signals which are detected bythe RF detector 112 associated with the transmitting tire monitor 106.The receiving RF detector 112 signals its detection of the RF signals byproviding the transmission indication on its associated conductor 114.

The RF decoder 122 is further configured to identify a position of atransmitting tire monitor on the vehicle in response to the transmissionindication received from an RF detector. Accordingly, the RF decoder 122includes a plurality of input circuits 123 coupled to the conductors 114which are in turn coupled to the RF detectors 112. A transmissionindication impressed on a conductor 114 is detected by an associatedinput circuit 123. In the illustrated embodiment, there is a one-to-onerelationship between input circuits 123 and RF detectors 112. In thismanner, the RF detector 112 which originated the transmission indicationmay be identified by the RF decoder determining which input circuit 123detects the transmission indication. In alternative embodiments, the RFdecoder 122 may include fewer than four input circuits 123 which aremultiplexed in some manner among the plurality of RF detectors 112. Forexample, a single input circuit 123 may be time shared among theplurality of RF detectors 112 to reduce the cost and complexity of theRF decoder 122.

The RF decoder 122 is electrically coupled with the RF circuit 120. Uponreceipt of RF signals at the RF circuit 120, the RF signals aredemodulated to extract the tire data contained within the RF signals. Insome applications, additional data decoding may be required afterdemodulation. The tire data in one exemplary embodiment includes a tiremonitor identifier, or unique identification code which uniquelyidentifies the tire monitor 106 which transmitted the RF signals. Inaddition, in this exemplary embodiment, the tire data also includes tirepressure data related to a sensed tire pressure of the tire 104 at whichthe transmitting tire monitor 106 is located. Alternative tire data maybe included or substituted for the tire pressure data, such as a numberof tire revolutions, tire temperature, and so forth.

After extracting the tire data from the RF signals, the tire data isconveyed from the RF receiver 120 to the RF decoder 122. The RF decoder122 associates the tire data with a position of the transmitting tiremonitor 106 on the vehicle 102. Position information is determined usingthe input circuit 123 and a transmission indication received over aconductor 114 from RF detector 112. The tire data and associated tireposition are conveyed from the RF decoder 122 to the controller 124.

The controller 124 controls the operation of the remote tire monitorsystem 100. The controller 124 is preferably a microcontroller includinga processor 128 and a memory 126. The processor 128 operates in responseto data and instructions stored in the memory 126 to control overalloperation of the system 100.

In the illustrated embodiment, the processor 128 stores position datafor a plurality of tire monitors 106 of the remote tire monitor system100. The controller 124 is electrically coupled to the RF decoder 122 toreceive tire data and position data from the RF decoder 122. In theillustrated embodiment, when tire data and position data are received atthe microcontroller 124, the processor 128 retrieves stored positiondata from the memory 126. In one embodiment, the position data arestored in association with a position on the vehicle, such as leftfront, left rear, right front or right rear. The received position datais compared with the stored position data. If there is no change, theposition data is not updated and further processing may occur using thereceived tire data. However, the processor 128 updates the position datafor the transmitting tire monitor 106 when the position of thetransmitting tire monitor 106 varies from the stored position data forthe transmitting tire monitor. Thus, the controller 124 includes amemory 126 and a processor configured to store in the memory 126position of the plurality of tire monitors 106 including the position ofthe transmitting tire monitor which originated the received positiondata.

In an alternative embodiment, the memory 126 is not used for storage ofposition data. Rather, the received tire data is associated by thecontrol unit 110 with the position information provided by thetransmission indication from a RF detector 112. The tire data and theposition information from the input circuit 123 are used together toproduce a display or alarm, if appropriate, by the system 100.Additionally, in still another embodiment, the tire data omits anyidentifying information for the transmitting tire monitor 106 and again,the tire data and the position information from the input circuit 123are used together to produce the appropriate display or alarm.

Completing the identification of the elements in FIG. 1, the vehicle 102further includes a CAN driver 130, a voltage regulator 132, power linenoise suppressor 134, and a battery 136. The battery 136 providesoperating power for electrical systems of the vehicle 102 including theremote tire monitor system 100. The battery 136 is a portion of theelectrical power system of the vehicle, which typically also includes analternator and other components. Such electrical power systems forvehicles are well known. The power line suppressor 134 reduces noise onthe power line from the battery 136. Noise may originate in otherelectrical components of the vehicle 102, such as the ignition system.The voltage regulator 132 receives the battery voltage or otheroperating voltage from the power line suppressor 134 and produces a wellregulated voltage for components such as the control unit 110 and CANdriver 130. The CAN driver 130 provides electrical interface with otherelements of a Controlled Area Network. Controlled Area Network or CAN isa serial communication protocol for data commonly used in automotive andother applications. The CAN bus 138 accessed by the CAN driver 130 isused to interconnect a network of electronic nodes or modules. The CANbus operates according to an adopted standard. In conjunction with aremote tire pressure monitor system 100, the CAN bus 138 may be used toconvey tire monitor data to other locations in the vehicle 102. Forexample, an alarm or a display (not shown) may be controlled to providea visual or audible indication to an operator of the vehicle 102 thatthe tire data indicates an out-of-range condition, such as low tirepressure.

In FIG. 1, the RF decoder 122 and the controller 124 are shown asseparate elements of the control unit 110. In alternative embodiments,they may be combined in a single processor or logic block or circuit.Any other illustrated elements or additional elements included toenhance the functionality of the system 100 may be integrated orcombined with other components of the system 100.

Further, the system 100 should not be restricted to use in conjunctionwith a CAN bus. In alternative embodiments, any other communicationsmedium may be employed for interconnecting the system 100 with otherelements of the vehicle 102. For example, communication buses inaccordance with the J-1850 or USB standards may be substituted, or thecontrol unit 110 may be directly hard wired with other elements of thevehicle 102. Still further, external communications may be omittedentirely so that the system 100 is completely self-contained.

FIG. 1 further shows a detailed view of one embodiment of an RF detector112 for use in the remote tire monitor system 100. The RF detector 112includes an antenna 140 to sense radio frequency (RF) signalstransmitted from the tire monitor 106, an amplifier 142, an envelopedetector coupled to the antenna 140 through the amplifier 142 and anoutput circuit 146 coupled to the envelope detector 144. The envelopedetector 144 includes a filter 149, a diode 150, a capacitor 152 coupledto ground and an amplifier 154. The RF detector 112 is powered from apower line 156 and a ground line 158 provided on the conductor 114 whichcouples the RF detector 112 to the input circuit 123 of the RF decoder122. To isolate the operational circuitry of the RF detector 112 fromnoise on the power line 156, the RF detector 112 further includes aresistor 160 and a capacitor 162 to ground.

The envelope detector 144 responds to the input signals received at theantenna and amplified by the amplifier 142 to produce at the outputcircuit 146 data corresponding to the envelope of the RF signalstransmitted by the tire monitors 106. Thus, the filter 148, diode 150and capacitor 152 together form a circuit coupled with the antenna 140to detect an envelope of electrical signals produced by the antenna inresponse to the RF signals. The envelope is itself an electrical signalwhich is amplified in the amplifier 154. The output signal from theamplifier 154 is applied to the base of a transistor 164. In response tothis signal at its base, the transistor 164 modulates a wireline signalon the conductor 114 in response to the envelope of the RF signalsreceived at the RF detector 112. That is, the signals applied at thebase of the transistor 164 control turn-on of the transistor 164,conducting current from its collector at the power node of the conductor114 to its emitter at the ground node of the conductor 114. As a result,the current in the conductor 114 will be modulated in response to the RFsignals received at the antenna 140 of the RF detector 112.

In one embodiment, to detect the modulated current, the input circuits123 of the RF decoder in the illustrated embodiment may include acurrent mirror which duplicates the current drawn from the input stageof the input circuit 123, coupled to the conductor 114. The outputcurrent from the current mirror in the input circuit 123 is provided toa resistor which converts the current signal into a voltage signal whichcan be read by the microcontroller 124. Suitable current mirror circuitsare within the purview of those ordinarily skilled in the art of circuitdesign.

In this manner, then, the signal provided on the conductor 114 forms atransmission indication indicating that the tire monitor 106 associatedwith the RF detector 112 has transmitted an RF signal which was detectedby the RF detector 112. Producing the transmission indication includesdetecting the envelope of the RF signals transmitted by the tire monitor106 and producing a wireline signal on the conductor 114 in response tothe envelope of the RF signals. In particular, in the illustratedembodiment, the wireline signal is produced by modulating a current in aconductor 114 coupled with the control unit 110. The control unit 110detects the modulation of the current to locate the transmitting tiremonitor 106.

Significantly, the RF detector 112 does not demodulate the datatransmitted by the tire monitor 106. Only the RF circuit 120 of thecontrol unit 110 demodulates the data to extract the contents of the RFsignal 106. The RF detector only senses the presence of the transmittedRF signals. This reduces the cost of the RF detectors 112 and theoverall cost of the remote tire monitor system 100.

Also, by modulating the current in the conductor 114, the RF detector'ssensitivity to noise is reduced. Noise will occur in the form of voltagespikes or pulses on the conductor 114. However, this noise will havelittle effect on the operation of the RF detector 112 and will havelittle effect on the current levels in the conductor. As a result, theconductor 114 can be, for example, a twisted pair of wire or any otherinexpensive two-wire cable. Coaxial cable or other shielded cable is notnecessary for implementing the system 100 using RF detector 112.

In alternative embodiments, the RF circuit 120 may be omitted. In suchan embodiment, the RF detectors 112 are used to detect the variations inthe radio frequency signals and modulate a wire line signal on theconductors 114. The RF decoder 122 in such an embodiment is configuredto demodulate the data in conjunction with the microcontroller 124.Current pulses on the conductor 114 are detected by the RF decoder 122and converted to voltage pulses. The voltage pulses can be read by themicrocontroller 124. In this manner, microcontroller 124 obtains thedata from the RF detectors and the RF decoder, without use of an RFcircuit 120. This has the advantage of eliminating the relativelyexpensive RF circuit. Further, this permits reduction in the transmitpower used by the tire monitors 106 to transmit the radio frequencysignals conveying the entire data. In some jurisdictions, substantiallyattenuated transmit power is required for applications such as tiremonitors. These low transmit power requirements may be satisfied whilestill providing reliable performance in the remote tire monitoringsystem 100 by use of the RF detectors 112.

In still other embodiments, the functionality described herein may beimplemented using a programmed computer or other processor operating inresponse to data and instructions stored in memory. The processor mayoperate in conjunction with some or all of the hardware elementsdescribed in the embodiments shown herein.

The disclosed tire monitor system may be used to provide an improvedauto learn or auto train method for automatically identifying positionsof a plurality of tire monitors on a vehicle. As noted above, previouslydevices such as a transponder or magnetic activation tools were used inthe car plant to train the control unit of the remote tire monitorsystem with identifiers for the wheel sensors or tire monitors. With thevehicle located in a training booth or activation area at the factory,the wheel sensors were activated in sequence and the control unit,expecting activated pressure transmissions in a certain order, learnedthe identification and position on the vehicle of the wheel sensors. Soas to prevent cross talk from other training booths, each activationarea is required to be RF shielded. Another method of training thereceivers was to use bar code readers to scan the identifiers of thewheel sensors and input this data into the receiver. All of thesemethods required an additional operation either manually or by automaticreaders. These operations add cost and potential for downtime.

In the illustrated embodiment of FIG. 1, no such tools are required. Inthe car plant at the end of the production line, a standard one to twominute dynamic test is used to test and calibrate steering, brakes etc.of the vehicle. For the illustrated embodiment, positions and identitiesof the four tire pressure monitor wheel sensors are automaticallylearned during this dynamic test.

This is achieved by placing the control unit or receiver in a “learnstate” at a dynamic test booth. The wheel sensors transmit either once aminute as in the normal mode, or in a special initial mode correspondingto a brand new, right out of the box state, transmitting more often, forexample every 30 seconds, or every 10 seconds.

For example, when the wheel sensors leave the manufacturer's productionline, they are placed in off mode. This mode means that each wheelsensor is dormant until it is activated by the closing of its motionswitch. Closing the motion switch is only achievable through centrifugalforce caused by spinning the tire monitor on a rotating wheel. Duringnormal operation, the wheel sensor, while driving, transmits tireinformation including supervisory tire pressure once every minute.However, in the illustrated embodiment, for the driving periods duringthe first 16 activations of the motion switch, the wheel sensor willtransmit the supervisory pressure data once every 30 seconds (to conformto United States regulatory requirements) or 10 seconds outside theUnited States. Other time intervals may be used. After the initial 16transmissions, or any other suitable number, the transmission intervalis changed to its normal mode value, such as one minute. This initialmode is known as factory test mode.

At the time of the dynamic vehicle test, the vehicle is accelerated,causing the wheel sensors to activate with the rotation of the wheelsand associated closure of their motion switches. When the wheel sensorsbegin transmitting tire pressure, say once every thirty seconds, eachsensor's identifier is transmitted by the sensor and is received up bythe RF circuit of the control unit. In this initial unlearned state, thereceiver loads the new identifier into memory, associating thetransmission with one of the four RF detectors. Only data received whichalso is synchronized to activity on one of the RF detector conductors isregarded as valid. Over the one to two minute duration of the dynamictest, each wheel sensor will transmit numerous times and the controlunit can verify the tire information, such as each wheel sensoridentifier, and associated wheel position. The control unit can thenload this data into non-volatile memory for subsequent normal use.

Key advantages of this auto-learn technique is the lack of anyadditional labor or equipment at the vehicle assembly plant, and thelack of a need for a transponder component or magnetic switch in thewheel sensor. Also there is no possibility of learning the wrong wheels,from other vehicles due to cross talk or of getting the wrong position.Thus, cost is reduced, operation is simplified and reliability isincreased. Using the illustrated embodiment of the tire monitor system,no additional activation or learning tools are required to train thecontrol unit with the wheel sensors' position on the vehicle. The onlydevice required to train the control unit is the standard dynamicvehicle test at the end of line test in the vehicle assembly plant.Because the training procedure can be carried out in parallel with thesteering and braking tests on the rolling road, and because of thefactory test mode feature, no extra time or cost is required to ‘autolearn’ the tire monitor system.

The illustrated embodiment further provides for automatic update of tiremonitor position information in the control unit upon replacement of oneof the tire monitors of the system. This would occur, for example, ifone of the wheels or tires of the vehicle is replaced. Due to the natureof the current embodiment, where the RF detectors are continuouslyindicating the position of the wheel sensors, a wheel sensor may bereplaced and detected by the control unit without the need for userintervention. In this case, where a new wheel sensor is put on a wheel,the control unit initially realizes it is receiving a wrong identifierfor the tire monitor, but still getting RF detector pulses from aparticular wheel position. In addition, the control unit detects thatthe previously stored identifier for that position is no longer beingreceived. Over a period of time, say ten minutes driving, the receiververifies it has stopped receiving a stored identifier and is nowreceiving a new ID for that position. After verification, the newidentifier is stored for that position and operation continues asnormal.

The big advantage of this is the lack of need for user intervention andelimination of the need for a service tool at each service location.Tire monitor position and identification is updated automatically.

FIG. 2 is a flow diagram illustrating an auto learn method for theremote tire monitor system of FIG. 1. The method begins at block 200. Atblock 202, one or more tires with new tire monitors are mounted on avehicle which includes a remote tire monitor system. In this embodiment,the tire monitors are in unused, out of the box condition from themanufacturer. The installation of block 202 may occur as part of thefinal assembly of the vehicle at the factory. Alternatively, theinstallation may occur when new tires are installed on the vehicle orwhen a remote tire monitor system is added to the vehicle.

At block 204, the dynamic vehicle test is initiated and, in response, atblock 206, the tire monitors begin transmitting radio frequency (RF)signals. The dynamic vehicle test is a test to check properfunctionality of the systems of the vehicle, including drive train andbrakes. Alternatively, any activity which causes the tire monitors tobegin transmitting may be substituted at block 204 to initiatetransmission at block 206. For example, the process of driving thevehicle from the end of the assembly line to a storage area or a finalcheckout area in block 204 may be adequate to begin transmission atblock 206. It is contemplated that the tire monitors each include amotion switch which activates the tire monitor in response to motion ofthe tire monitor on the wheel of the vehicle.

Further, at block 206, the tire monitor begins transmitting at a testmode interval, such as once every 30 or 60 seconds. This aspect may beomitted but adds convenience for initializing the tire monitor system.After initialization, the interval may be reduced to reduce power drainfrom the battery which powers the tire monitor.

After transmission of the RF signals at block 206, the RF signals arereceived by a receiver of the remote tire monitor system at block 208.The RF signals are demodulated, decoded and otherwise processed toextract the data conveyed on the RF signals. For example, the tiremonitor may modulate a carrier signal using data corresponding topressure of the tire or a tire monitor identifier. The receiver of theremote tire monitor system demodulates the received RF signals toreceive the data. At block 212, the data including a tire monitoridentifier, if any, is provided to a control unit of the remote tiremonitor system.

Meanwhile, the same RF signals received and demodulated at blocks 208,210 are detected at block 214. In the preferred embodiment, the RFsignals are received without demodulation, for example, using a detectorof the type illustrated above in conjunction with FIG. 1. Other suitableRF detectors may be used. At block 216, in response to the detected RFsignals, a transmission indication is provided to the control unit. Thetransmission indication indicates to the control unit which RF detectorof the vehicle detected the RF signals transmitted by the tire monitorand received by the receiver at block 208.

At block 218, identification information associated with the tiremonitor is stored. In one embodiment, the data forming the identifiertransmitted by the tire monitor and received by the receiver of theremote tire monitor system is stored in memory. Other types and formatsof identification information may be stored. For example, the controlunit may store an RF detector indicator which indicates which RFdetector detected the received RF signals.

In this manner, the described method provides automatic learn capabilityin a remote tire monitor system. No manual intervention is necessary forthe control unit to identify and store the identities and locations ofindividual tire monitors on the vehicle. This reduces time and costassociated with initiating operation of the remote tire monitor system.

FIG. 3 is a flow diagram illustrating an auto learn method for theremote tire monitor system of FIG. 1. The method of FIG. 3 starts atblock 300.

At block 302, RF signals transmitted by a tire monitor associated with awheel of a vehicle are received by a receiver of the remote tire monitorsystem. At block 304, the RF signals are demodulated, decoded andotherwise processed to extract the data conveyed on the RF signals. Forexample, the tire monitor may modulate a carrier signal using datacorresponding to pressure of the tire or a tire monitor identifier. Thetire monitor identifier may be a serial number or other unique ornearly-unique data associated with the tire monitor. For example, thetire monitor identifier may be multiple bit data stored in the tiremonitor at the time of manufacture of the tire monitor. The receiver ofthe remote tire monitor system demodulates the received RF signals toreceive the data. At block 306, the data including a tire monitoridentifier, if any, is provided to a control unit of the remote tiremonitor system.

Meanwhile, the same RF signals received and demodulated at blocks 302,304 are detected at block 308. In the preferred embodiment, the RFsignals are received without demodulation, for example, using a detectorof the type illustrated above in conjunction with FIG. 1. Other suitableRF detectors may be used. At block 310, in response to the detected RFsignals, a transmission indication is provided to the control unit. Thetransmission indication indicates to the control unit which RF detectorof the vehicle detected the RF signals transmitted by the tire monitorand received by the receiver at block 302.

At block 312, stored identification information is retrieved from memoryat the control unit. In the illustrated embodiment, the identificationinformation is stored at a memory location associated with thetransmission indication or RF detector. Thus, the control unit receivesa wireline indication from a receiving RF detector that a transmissionhas been received. Using the wireline indication, the control unitselects the memory location from which previous identificationinformation is retrieved.

At block 314, the control unit determines if the identifier receivedfrom the transmitting tire monitor matches the stored identificationinformation. In this application, a match may mean a bit-by-bit match ofreceived and stored data or some other level or association between thereceived data and the stored data. If the data match, at block 316, thetire information such as pressure data are updated. For example, in oneembodiment, tire pressure data are stored along with the identificationinformation for the tire monitor. If the received tire pressure datavaries by a predetermined amount from the stored tire pressure data, thereceived tire pressure data is stored and an alarm or other userindication is generated.

At block 318, if there is no match between the received identifier andthe stored identification information, the method waits for receipt ofan additional transmission associated with this RF detector. Preferably,the tire monitor transmits pressure data and a tire monitor identifierperiodically, such as once per minute. Upon receipt of a subsequenttransmission, at block 320, the method attempts to verify the previouslyreceived tire monitor identifier. This is done by comparing the newlyreceived tire monitor identifier and the previously received tiremonitor identifier to determine if there was an error in communicationof the previously received tire monitor identifier. In some embodiments,multiple subsequent transmissions may be received for comparison. Ifthere is no verification, at block 322, the mismatched transmissionreceived at block 302 is discarded. This condition indicates that thesame tire monitor continues to transmit, and the mismatched transmissionwas received with an error.

If at block 320 the newly received data verify the previously receiveddata, the identification information stored for this RF detector isupdated with the tire monitor identifier from the received transmission.This condition indicates that the tire monitor has been changed and iscommunicating reliably. In this manner, the illustrated system andmethod provide automatic update capability after a tire monitor has beenchanged. This may occur if the tires of the vehicle are rotated or ifone or more tires is replaced. There is thus no need to manuallyintervene for the remote tire monitor system to update the identitiesand locations of the tire monitors on the vehicle.

FIG. 4 is a block diagram of a vehicle 400 with a remote tire monitorsystem 402. In the exemplary embodiment of FIG. 4, the vehicle 402includes wheels 404, 406, 408, 410. Each wheel includes a tire mountedon a rim. In other embodiments, the vehicle 400 may have other numbersof wheels. For example, in one particular embodiment, a truck has 18wheels.

The remote tire monitor system 402 includes a control unit 412, a frontdetector 414 and a rear detector 416. The front detector 414 iselectrically coupled to the control unit 412 by a cable 418. Similarly,the rear detector 416 is electrically coupled to the control unit 412 bya cable 420.

The remote tire monitor system 402 further includes a tire monitorassociated with each wheel of the vehicle 400. Thus, a tire monitor 424is associated with wheel 404; tire monitor 426 is associated with wheel406; tire monitor 428 is associated with wheel 408; and tire monitor 430is associated with wheel 410. The tire monitors are generally of thetype described herein and are configured to detect a tire condition suchas tire pressure and to occasionally transmit a transmission includingtire data, such as tire pressure data and identification informationuniquely identifying the respective tire monitor.

In the illustrated embodiment, the front detector 414 is positionedproximate the left front wheel 404. For example, the front detector 414may be mounted in the wheel well adjacent the wheel 404. Similarly, therear detector 416 is positioned near the left rear wheel 408, such as inthe wheel well adjacent the wheel 408. With this mounting configuration,the front detector 414 is positioned to detect transmissions from thepair of tire monitors 424, 426 associated with the front wheels 404,406. The front detector 414 is proximate the left front tire monitor 424and distal the right front tire monitor 426. Similarly, the reardetector 416 is positioned to detect transmissions from the left reartire monitor 428 and the right rear tire monitor 430. The rear detector416 is positioned proximate the left rear tire monitor 428 and distalthe right rear tire monitor 430.

The illustrated embodiment is exemplary only. In FIG. 4, the detectors414, 416 are designated for detecting radio frequency transmissions fromthe front wheels 404, 406 and the rear wheels 408, 410, respectively. Inalternate embodiments, the RF detectors 414, 416 may be positioned todetect RF transmissions from the left side wheels 404, 408 and the rightside wheels 406, 410 respectively. Similarly, while in FIG. 4 the frontdetector 414 is positioned in proximity to the left front wheel 404,away from the right front wheel 406, this positioning may be reversed sothat the front detector 414 is positioned near the right front wheel406, such as in the left front wheel well. In the same way, the reardetector 416, shown in FIG. 4 in proximity to the left rear wheel 408,may be positioned in proximity to the right rear wheel 410. Actualpositioning of the RF detectors 414, 416 is not important. Rather, therelative signal strength or frequency of reception of RF transmissionsfrom tire monitors is what is measured by the detectors 414, 416 inconjunction with the control unit 412. It is important that each RFdetector be positioned on one side or end of the car, away from thecenterline, so that the relative signal strength or number oftransmissions received by the RF detector from each of its associatedpair of tire monitors can be determined.

The control unit 412 includes a receiver to receive radio frequencytransmissions from tire monitors of the tire monitor system 402, acontroller 432 and a memory device 434. The controller 432 forms aprocessing means and may be any suitable control device such as amicroprocessor, microcontroller, application specific integrated circuit(ASIC) or logic device coupled together to perform the necessaryfunctions described herein.

The memory device 434 forms a memory means for storing data andpreferably is formed of semiconductor memory. In the illustratedembodiment, the memory device of the control unit 412 includespersistent memory or nonvolatile memory such as an E²PROM, and workingmemory such as random access memory (RAM). For example, the persistentmemory may be used to stored tire identifiers and pressure data overextended periods of time, such as when the vehicle 400 is parked. TheRAM may be organized as an array which stores counter values associatedwith tire monitor identifiers and tire monitor positions, as will bedescribed in greater detail below.

FIG. 5 is a flow diagram illustrating operation of one embodiment of aremote tire monitor system. The method illustrated in FIG. 5 may be usedin conjunction with a remote tire monitor system of the type illustratedin FIG. 4. The method embodiment in FIG. 5 allows a control unit of sucha system to automatically learn the positions of the tire monitors ofthe system on the vehicle, referred to as a learn method or learnroutine. This determination is made after receiving several transmittedframes of tire data from the respective tire monitors of the system. Thecontrol unit establishes an array of data in working memory and uses thedata of the array to determine the position information for each tiremonitor in the system. An example array of data is illustrated below.FrontRFD Rear RFD Total RF_FrameCounter id1 22 2 22 id2 12 4 23 id3 2 2020 id4 1 10 20

In this example, rows of the array are defined by the identificationinformation for each tire monitor from which data are received. In theexample above, the identification information is listed as “id1,” “id2,”etc. However, in a more typical example, the identification informationwill be a numeric value forming a unique identifier or identificationcode of a transmitting tire monitor. The identification code istypically transmitted along with the tire pressure or other tire data bythe tire monitor in a transmission frame. The exemplary array is shownwith four rows, one for each tire monitor of the vehicle in thisexample. The array may also be formatted with additional rows to recorddata for additional transmitting tire monitors whose transmissions arereceived by the controller.

In the example array above, the columns of the array correspond to framecounter values which count the number of frames received at therespective RF detector of the system. Thus, in this example, a framelabeled with tire monitor identifier id1 has been received at the frontRF detector 22 times. A frame with the same identifier id1 has beenreceived at the rear RF detector two times, and so on. The count labelTotalRF_FrameCounter is a count of the total number of frames receivedby the receiver of the controller from the identified tire monitor. Thetotal frame counts recorded in this column is always greater than orequal to an RFD frame counter because the receiver has greatersensitivity than the RF detectors and detects transmissions that aremissed by the RF detectors.

The method of FIG. 5 begins at block 500. The method of FIG. 5 shows thelearn routine on the production line, when the tires of the vehicle arefirst assembled with the tire monitors and added to the remote tiremonitor system. At block 502, it is determined if tire identifiers arealready stored in electrically erasable (E²) memory. This memory isnonvolatile or persistent memory which retains data stored therein evenwhen power is removed from the memory. In the illustrated system, afterinstallation on a vehicle, the persistent memory is empty. As soon astire identifiers are received and verified according to the procedure ofFIG. 5, the tire monitors are stored in the persistent memory. Thus,block 502 determines if this is the first time the tire monitor systemhas been operated after installation on a vehicle. If so, no tiremonitor identifiers will be stored in the persistent memory and the “no”path will follow to block 602. If tire identifiers are already stored inthe persistent memory, the “yes” path is followed to block 504.

At block 504, it is determined if a frame of data has been received. Ifnot, control remains in a loop including block 504 until a frame of datahave been received. As indicated above, each frame of data transmittedby a tire monitor typically includes data corresponding to the tireidentifier which uniquely identifies the transmitting tire monitor andtire data, such as data corresponding to the measured tire pressure ofthe tire. Other information, such as a header or synchronization datamay be transmitted as well.

Once a frame of data has been received at block 504, the tire monitoridentifier contained in the frame of data is extracted and compared withother already-received identifiers stored in the list in working memory.If the extracted tire identifier is not present in the list, block 506,it is added to the list, block 508. Control then proceeds to block 510,where the relevant wheel position counters are incremented. As notedabove, each identifier has three associated counters. One counter eachis associated with each RF detector of the system and stores datacorresponding to the number of transmissions detected by that respectiveRF detector. The third counter counts the total frames received from anidentified tire monitor, and is incremented after a frame is received atthe receiver of the controller. Thus, the relevant wheel positioncounters that are incremented at block 510 include the total RF framecounter and the frame counter corresponding to the front RF detector orthe rear RF detector.

At block 512, a test is performed to determine if the specified criteriahave been fulfilled. First, it is determined if four tire identifiers inthe list have Total RF Frame counter values that are greater than apredetermined number, 20 in this example. That is, before applying thepass criteria, at least four tire identifier counters must have a valueof 20 or greater. This test is implemented to ensure that there is astrong signal from a tire monitor and to eliminate any wrong orincorrect tire identifiers being added to the system. If the receivedsignal from a tire monitor is weak, it will likely be received only afew times, rather than 20 or more times. Any other suitable number maybe substituted for the predetermined number 20. Reducing the number willincrease the speed at which the tire monitor positioning is learned bythe system, but may increase the likelihood of incorrect tire monitorposition learning.

According to the second criterion of the illustrated embodiment, thecounter for the front RF detector must be larger than the counter forthe rear RF detector for two different tire identifiers out of the four.According to the third criterion, it is determined if the the framecounter for the rear RF detector stores a value larger than the front RFdetector frame counter for the two remaining tire identifiers in thelist. If these criteria are not fulfilled using the tire identifiers inthe list, control returns to the block 504 to await receipt ofadditional frame of data.

If these three criteria are fulfilled, however, at block 514, two tireidentifiers are selected from the list for the front axle of thevehicle, according to the second criterion above, and two tireidentifiers are selected from the list for the rear axle, according tothe third criterion above. Thus, at block 518, the method has chosenfour tire identifiers with a total RF frame counter value higher than 20and has distinguished the selected tire identifiers between the front ofthe vehicle and the rear of the vehicle by using the front frame countervalue and rear frame counter value. For example, using the values shownin the example list above, the tire identifiers corresponding to thetire monitors positioned at the front of a vehicle are tire identifiersid1 and id2. The tire identifiers corresponding to tire monitorspositioned at the rear of the vehicle are id3 and id4.

Beginning at block 516, the method identifies the right and left tiremonitor for each axle. First it is determined if, among the identifiedtire identifiers from the list for each of the front and rear axles, oneRF detector counter value has a higher frame counter value than theother. If not, the method cannot distinguish the two tire monitors onthe axle. Control returns to block 504 to await receipt of additionalframes of data. If the criterion of block 516 is met, at block 518 thetire indicator with the higher RF detector frame counter value isselected to be on the same side of the vehicle as the RF detector forthat end of the vehicle. Thus, in FIG. 4, among the front wheels 404,406, the tire identifier associated with the larger valued RF detectorcounter is selected to correspond to tire monitor 426. Similarly, thetire identifier having the lower valued RF detector counter value isselected to be associated with the tire monitor 424. Alternatively, if,as is suggested in FIG. 5, those RF detectors 414 and 416 are positionedon the left side of the vehicle 400, then of the tires of tireidentifier selected at block 514, the larger valued RF detector framecounter is associated with the left-hand side tire monitor for bothaxles. In the illustration of FIG. 4, if the RF detector 414 wereinstead mounted on the left-hand side of the vehicle 400, the largervalued tire identifier would be selected to be associated with tiremonitor 424 and the larger valued RF detector frame counter would beselected to be associated with tire monitor 428. Using the example listof data above, and assuming that both tire monitors are on the left-handside of the vehicle, the method would select id1 for the left front tiremonitor and id2 for the right front tire monitor. Similarly, the methodwould select id3 for the left rear tire monitor and id4 for the rightrear tire monitor.

At block 520, the four selected tire identifiers are stored innon-volatile memory such as the E²PROM or other persistent memorydescribed above. During subsequent operation of the tire monitor system,as new frames of tire data are received, the tire identificationinformation contained in the frame will be compared with one of theselected in store for tire identifiers. If there is a match, the tirepressure information or other tire data contained in the frame will beused to update the current tire pressure information. At block 522, thelearn routine illustrated in FIG. 5 is exited and the method of FIG. 5terminates.

FIG. 6 illustrates a method for the remote tire monitor system to learnthe positioning of tire monitors on a vehicle during a normal drivingoperation. The method begins at block 602, which is accessed afterdetermining at block 502 (FIG. 5) that tire monitor identifiers havealready been stored in the persistent memory of the system.

At block 602, the tire monitor values stored in the persistent memoryare inserted into the list or array in working memory. The Total RFFrame Counter, the front RF detector counter value (for identifierswhich were in the front) and the rear RF detector counter value (foridentifiers which were in the rear) for each of these array entries ispreloaded with a predetermined value, such as 5. Storing preloadedvalues such as this gives a weighting to the tire identifiers alreadystored in the persistent memory and copied into the working memoryarray. The benefit of weighting the preloaded tire monitor values in thearray in this manner is to reduce the likelihood that a tire monitor onan adjacent vehicle will be detected and selected as one of the fourtire monitors of the vehicle. This could occur, for example, if morethan one vehicle with comparable systems are parked adjacent each other,such as the end of an assembly line or in another location. Further,weighting the preloaded tire monitor values reduces the time requiredfor the learn process so that reliable information can be given to thedriver sooner. This process happens every time the vehicle is startedand a new journey is begun.

At block 604, it is determined if a frame of data has been received. Ifnot, control remains in a loop including block 604 until a frame of datais received. Once a frame of data has been received, control proceeds toblock 606.

At block 606 it is determined if the tire monitor identifier containedin the received frame is already stored in the persistent memory orE²PROM. If not, at block 608 the received tire monitor identifier isadded to the working list of tire identifiers in working memory. Controlproceeds to block 610.

At block 610, the relevant wheel position counters are incremented.Operation here is similar to the operation at block 510, FIG. 5. Theworking list of data includes columns for each of the front and rear RFdetector counters and a total RF frame counter. At block 610, the totalRF frame counter corresponding to the received tire identifier isincremented. Also at block 610, the counter corresponding to the frontor rear RF detector is incremented, depending on which RF detectorsensed or detected the transmission from the transmitting tire monitor.

At block 612, three criteria are tested to determine if sufficientframes of data have been received to reliably distinguish front fromrear tire monitor positions. Operation of block 612 is similar to theoperation of block 512, FIG. 5. At block 614, two tire identifiers areselected to correspond to the front end of the vehicle and two tireidentifiers are selected to correspond to the rear end of the vehicle.At block 612, if all three criteria are not fulfilled, control returnsto block 604 to await the receipt of additional frames of data.

At block 616, it is determined if, for each of the front and rear setsof tire monitors, one tire monitor has a higher RF detector countervalue. If not, control returns to block 604 to await the receipt ofadditional data. If so, at block 618, the front and rear selected tiremonitor pairs are each sorted among right and left tire monitors,selecting a left front, right front, left rear and right rear tiremonitor. At block 620, the four tire monitor identifiers are stored innon-volatile or persistent memory, along with position information forthe tire monitor. The learn routine of FIG. 6 is then exited at 622.

From the foregoing, it can be seen that the present embodiments providea method and apparatus which automatically conveys wheel position anddata to a receiver in a vehicle. Even after changes in tire position dueto tire rotation or replacement of a tire, the system automaticallyre-learns the position of the tires on the vehicle. No externalactuation is required. Interference and cross talk are minimized bylocating RF detectors in close proximity to the tire monitors. Bysharing one RF detector between the front wheels and one RF detectorbetween the rear wheels, the required number of RF detectors is reducedalong with the required cabling and the concomitant cost, weight anddifficulty of installation of the system. Further, the system providesautomatic learn capability for learning and updating the identities oftire monitors on the vehicle without manual intervention.

While a particular embodiment of the present invention has been shownand described, modifications may be made. For example, while theexemplary embodiment counts received transmissions from tire monitors ofthe system, other embodiments may use alternate methods or detect othersignal parameters to identify tire monitor positions in the system.Also, while the two learn methods of FIGS. 5 and 6 are generallysimilarly for both the learn method in the production line and the learnmethod during normal driving, other method steps or test criteria may besubstituted to change the two methods, accounting for the differingenvironments in which each method is practiced. It is therefore intendedin the appended claims to cover all such changes and modifications whichfall within the true spirit and scope of the invention.

In addition to the left/right determination described in conjunctionwith FIGS. 5 and 6, various other left/right determinations arepossible. In one embodiment, the remote tire monitor system 402 may beconfigured to detect the relative signal strength received by the RFdetectors 414, 416. In other embodiment, the control unit 412 may beconfigured to detect the relative signal strength received by the RFreceiver.

FIG. 7 is a block diagram of a vehicle 700 with a remote tire monitorsystem 702. In the exemplary embodiment of FIG. 7, the vehicle 700includes four wheels 704, 706, 708, 710. In other embodiments, thevehicle 700 may have other numbers of wheels. The remote tire monitorsystem 702 includes a front RF detector 714. The configuration of theremote tire monitor system 702 is not limited thereto, and various otherconfigurations such as a single rear RF detector, a single left RFdetector and a single right RF detector are possible. The remote tiremonitor system 702 includes a tire monitor associated with each wheel ofthe vehicle 700. Specifically, a tire monitor 724 is associated with awheel 704; tire monitor 726 is associated with a wheel 706; tire monitor728 is associated with a wheel 708; and tire monitor 730 is associatedwith a wheel 710.

The remote tire monitor system 702 includes a control unit 712. Thecontrol unit 712 includes an RF receiver such as the RF receiver 101 ofFIG. 1. In other embodiments, the RF receiver may include a receivedsignal strength indicator circuit. The front detector 714 iselectrically coupled to the control unit 712 by a cable 718. The cable718 may use one of the power lines distributed in the vehicle 700. Thefront detector 714 is positioned proximate the left front wheel 704. Forexample, the front detector 714 may be mounted in the wheel welladjacent the wheel 704. While the front detector 714 is positioned inproximity to the left front wheel 704, away from the right front wheel706, this positioning may be changed so that the front detector 714 ispositioned near the right front wheel 706, such as in the right frontwheel well in other embodiments.

With this mounting configuration, the front detector 714 is positionedto detect transmissions from the pair of tire monitors 724, 726associated with the front wheels 704, 706. Alternatively, oradditionally, the front detector 714 also may be operable to detecttransmission from the pair of tire monitors 728, 730 associated with therear wheels 708, 710.

Using the front detector 714, the remote tire monitor system 702operates as follows. When any tire monitor transmits data by emitting anRF transmission, the front detector 714 detects the burst of RF energy.The front detector 714 responds to the RF energy by modulating thesignal on the cable 718 to the control unit 712 with the envelope of thetransmitted data as described above in conjunction with FIG. 1. Thecontrol unit 712 detects this modulation as transmission indications.

Based on the detected modulations, the control unit 712 determines frontand rear position information. Because the front detector 714 ispositioned proximate the front tire monitors 724, 726 and distal fromthe rear tire monitors 728, 730, the front detector 714 may receive theRF transmissions from the rear tire monitors 728, 730 less frequentlythan the front tire monitors 724, 726. As a result, the control unit 712detects a smaller number of modulations from the rear tire monitors 728,730 than that from the front tire monitors 724, 726. By counting thedetected modulations, the control unit 712 may assign identifiers with agreater number of detected modulations to front wheels. Conversely, thecontrol unit 712 may assign identifiers with a smaller number ofdetected modulations to rear wheels.

FIG. 8 is a flowchart illustrating one embodiment of a method fordetermining position information of the remote tire monitor system 702during an auto learn mode. The operation of the remote tire monitorsystem 702 is described only for convenience of discussion and variousother remote tire monitor systems are possible. Blocks 800 to 810 may besubstantially similar to the blocks 500-510 of FIG. 2. At blocks 800 to810, the control unit 712 receives a number of frames of data from thetire monitors 724-730 and extracts identifiers from the data. Thecontrol unit 712 performs an auto learn mode as described in conjunctionwith FIGS. 2 and 5. After performing an auto learn mode for the remotetire monitor systems 702, the control unit 712 automatically learns thepositions of the tire monitors of the system on the vehicle. The controlunit 712 establishes an array of data in working memory 734. The data ofthe array includes identifiers of each tire monitor and count values ofthe detected modulations. Unlike the remote tire monitor 402 of FIG. 4,the remote tire monitor 702 may use two position counters associatedwith each identifier. One counter is associated with the front RFdetector 714, and the other counter is associated with counting thetotal frames received from an identified tire monitor. This total framesmay be received by the receiver of the control unit 712 having a higherlevel of sensitivity. By way of example only, the memory 734 may storethe array of data as follows. FrontRFD Total RF_FrameCounter id1 22 22id2 12 23 id3 6 20 Id4 1 20

At block 812, a test is performed to determine if four tire identifiersin the list have Total RF Frame counter values that are greater than apredetermined number, for example, 20. The fulfillment of this testindicates that there is a strong signal from each tire monitor, whichreduces possible errors based on weak signals. If this test isfulfilled, counter values of four tire monitors are compared todetermine position information at block 814. The control unit 712compares the counter values of the four identifiers and selects twoidentifiers for a front axle and the other two identifiers for a rearaxle at block 814. Due to the location of the RF detector 714, the twoidentifiers for the front axle have higher counter values than those forthe rear axle. The control unit 712 has default setting information ofthe RF detector configuration such as left front location of a single RFdetector. Thus, the control unit 712 assigns the two identifiers havingthe higher counter values to the front axle. The other two identifiersare assigned to the rear axle. In the foregoing example array, thecontrol unit 712 selects the identifiers id1 and id2 for the front axleand the identifiers id3 and id4 for the rear axle. At block 816, the twoidentifiers id1 and id2 for the front axle are compared and theidentifiers id3 and id4 for the rear axle are compared, respectively. Atblock 818, for each axle, the identifier with the higher counter valueis determined to be the same side as the side where the RF detector ismounted. Specifically, the identifier id1 is determined to be the leftside and the identifier id2 the right side. Likewise, the id3 isdetermined to be the left side and the id4 the right side.

At block 820, the four identifiers id1-id4 are stored in the memory 734.As a result, the control unit 712 is able to automatically determine theposition information of the four tire monitors 724-730 with the singleRF detector 714. It is important to position the RF detector 714off-center, i.e., proximate the left side or the right side todistinguish the left position from the right position.

In another embodiment, to improve accuracy of the positiondetermination, the control unit 712 may store configuration informationof the RF detector 714 and the tire monitors 724-730. As noted above, itmay be programmed to store the setting of the RF detector 714, i.e., thefront left location. Further, the control unit 712 may store informationconcerning each distance between the RF detector 714 and each tiremonitor 724-730, d1, d2, d3 and d4. The control unit 712 may or may notuse the information d1˜d4. When there is a substantial difference amongthe counter values of the identifiers, the control unit 712 may not usethe distance information d1˜d4 for determining the position. However, ifthe difference between the counter values is small, the control unit 712may retrieve the stored distance information and determine the positionbased on the counter values and the distance information. For example,in the remote tire monitor system 702 of FIG. 7, the distanceinformation d1˜d4 has the relationship of d4>d3>d2>d1. The countervalues may be inverse-proportional to the distances d1˜d4. With thedistance information, the accuracy of the system operation maysubstantially improve. This has a particular advantage for a remote tiremonitor system with more than four wheels. For example, trucks havingtwo front wheels disposed adjacent each other on each side and/or acenter wheel between a front wheel and a rear wheel may rely on thedistance information to improve accuracy of the position determination.

The remote tire monitor system 702 described above operates such thatthe RF detector 714 receives the RF transmissions from the rear tiremonitors 728, 730. In other embodiment, the front RF detector 714 maynot receive the RF transmissions from the rear tire monitors 728, 730.As noted above, the front detector 714 may be an inexpensive, small RFdetector to minimize expenses for implementing the tire monitor system702. The front detector 714 may not be sensitive enough to detect the RFtransmissions from the rear tire monitors 728, 730. Alternatively, oradditionally, the vehicle 700 may have a long body with a substantialdistance between the front wheels and the rear wheels such as limousine,trailers and trucks. In those cases, the front detector 714 may notdetect the RF transmission when the rear tire monitors 728, 730 transmitthe RF transmission. The control unit 712 also detects no modulationthat results from the RF transmission of the rear tire monitors 728,730. The control unit 712 assigns identifiers with any detectedmodulations to front wheels, whereas it assigns identifiers with nodetection to rear wheels. As a result, the control unit 712 is able todetermine front and rear position information with the single RFdetector 714.

Where the RF detector 714 detects the RF transmissions only from thefront tire monitors 724, 726, the control unit 712 performs an autolearn mode and establishes an array of the four identifiers id1˜id4. Twocounters may be used to count the total frames received from theidentified tire monitors. By way of example, the array of theidentifiers may be illustrated as follows. FrontRFD TotalRF_FrameCounter id1 22 22 id2 19 23 id3 0 20 id4 0 20The control unit 712 may use data of the array to determine front andrear position information of the remote tire monitor system 702. If thecontrol unit 712 detects no modulation, it may select and assign twoidentifiers id3 and id4 to the rear tire monitors 728, 730.

After determining the front and rear position, the left and rightposition information needs determination to complete the automaticrecognition of the tire monitor positioning. For the rear tire monitors728, 730, the control unit 712 may not use the data of the array becauseof no detection of the RF transmissions. For the front tire monitors724, 726, the control unit 712 may not again use the data of the arraybecause the difference in the counter values may be unrecognizable orsmall so that it may cause erroneous determination of the position. As aresult, the control unit 712 may not be able to determine the left/rightposition based on the counter values. Alternatively, or additionally,when the front detector 714 receives the RF transmission from the reartire monitors 728, 730 as described above, accurate left versus rightdetermination may not be made based on comparison of the counter values.For example, the counter values may have only minor differences.

Various methods for determining the left and right position informationare available. For example, the determination of the left and rightposition is made based on a received signal strength, acceleration,phase differences, tire pressure changes, etc. Other known methods arepossible. These methods are combined with the front/rear determinationmethod using the single RF detector to complete the automatic locationof the tire monitor positioning.

FIG. 9 is a flowchart illustrating operations of the remote tire monitorsystem 702, which determines the left and right position informationbased on a received signal strength. When the tire monitors 724, 726,728, 730 transmit signals, the RF receiver and/or the RF detector 714may receive the signals at blocks 902 and 908. The RF receiverdemodulate the RF signals to extract the tire monitor identifiers atblock 904 and provides the identifiers to the control unit 712 at block906. The RF detector 714 detects RF transmissions and modulates thecable 718 with the envelop at block 910. The control unit 712 associatesthe identifiers with detected modulation generated by the RF detector atblock 912. For example, the control unit 712 may count a number ofdetected modulations and establish an array of the identifiers and thenumber of detected modulations. At block 914, the control unit 712determines the front and rear position information based on the numberof detected modulations. Specifically, the control unit 712 operatessuch that the two identifiers with the greater number of detectedmodulations are assigned to front wheels and front tire monitors 724,726.

In addition to demodulation of the received RF signals, the RF receiveris operable to generate a received signal strength indicator (“RSSI”)signal. For this reason, the RF receiver may include an RSSI circuit anddemodulating and decoding circuitry to extract the identifiers. The RSSIcircuit generates the RSSI signal of the RF signals received at the RFreceiver at block 905. Various other RSSI circuits are possible as longas they detect the relative signal strength from tire monitors. The RSSIcircuit provides an RSSI signal to other circuits such as a signaldetector circuit. The signal detector circuit may include a peakdetector, a droop detector or a negative peak detector, etc. By way ofexample, the RF receiver includes a peak detector which is operated atblock 907. The peak detector outputs a peak received signal strengthsignal to a processor 732 of the control unit 712. The detaileddescription on the peak detector is provided in the copendingapplication Ser. No. 10/125,043, which is incorporated herein byreference in its entirety. In one embodiment, the processor 732 mayoperate such that it develops a running average of the peak RSSI valuesfor each wheel. At block 916, the control unit 712 retrieves the runningaverage of the peak RSSI values associated with the identifiers of thetire monitors 724, 726, 728, 730. At block 917, the control unit 712compares the running average of the peak RSSI values and determines twoidentifiers with greater RSSI values.

At the next block 918, the control unit 712 determines whether the RFreceiver and/or antenna 704 are positioned closer to the left wheels ofthe vehicle. Upon determination that the RF receiver and/or antenna 704are positioned closer to the left wheels, the control unit 712 assignstwo identifiers with the greater peak RSSI values to left wheels atblock 924. In other embodiment, the location of the RF receiver and/orantenna may be preprogrammed in the control unit 712. If the RF receiverand/or antenna are not positioned closer to the left wheels, the twoidentifiers with greater peak RSSI values to the right wheels at block922. At blocks 922 and 924, the control unit 712 completes thedetermination of the front left and the rear left wheels as well as therear left and the rear right wheels. At block 926, auto-location of thefour tire monitors 724, 726, 728, 730 is completed.

Alternatively, or additionally, the RSSI circuit of the RF receiver mayfurther permit the control unit 712 to determine additional positioninformation. For example, if the RF detector 714 does not properlyoperate, the control unit 712 may not receive any RF transmissions fromthe RF detector 714. For example, the array of the identifier in theworking memory 734 may be illustrated as follows. FrontRFD TotalRF_FrameCounter Id1 2 22 Id2 1 23 Id3 0 20 Id4 0 20Because the Total RF_FrameCounter exceeds a predetermined threshold, forexample, 20, the control unit 712 is able to determine that the tiremonitors 724-730 are transmitting tire data and properly working. Forthe same reason, the control unit 712 is able to determine that the RFdetector 714 is not properly operating. The control unit 712 may haveestablished another array of identifiers with the relative signalstrength. For example, the control unit 712 may increment a countervalue for each identifier each time the greatest RSSI value is receivedwith that identifier. Based on such counter values, the control unit 712may determine position information of the tire monitors. In FIG. 7, theRF receiver and/or antenna 704 are positioned closer to the left reartire monitor 726. The control unit 712 assigns the identifier with thelargest counter value to the left rear tire monitor 726, the secondlargest counter value to the left front tire monitor, and the smallestcounter value to the right front tire monitor. This is possible becausethe RF receiver has a greater sensitivity than that of the RF detector714.

In other embodiment, to determine left and right tire position, anacceleration signal from an acceleration sensor may be used. When a tirerotates, tire monitors experience two types of acceleration, centrifugalacceleration and tangential acceleration. The centrifugal accelerationis dependent upon the maximum vehicle speed. The tangential accelerationexperienced by the tire monitor develops at the periphery of rotatingtires. The centrifugal acceleration and the tangential accelerationsgenerate along two orthogonal axes.

Each tire monitor includes an acceleration sensor to detect accelerationvalues. The acceleration values include the polarity of the tangentialacceleration, phase difference between two types of acceleration, etc.The acceleration sensor may be a dual-axis sensor or a tri-axis sensor,which detects the acceleration values developing along two axes or threeaxes. The acceleration sensor generates signals representing theacceleration values. In one embodiment, the acceleration sensor detectsthe polarity of the tangential acceleration and generates a signalrepresenting the polarity. The wheels on the left side and the rightside of the vehicle are normally configured to rotate in oppositedirections. As a result, the tire monitors on the left side and theright side of a vehicle experience the tangential acceleration that isoppositely directed. For example, the left tire monitors 724, 728 andthe right tire monitors 726, 730 transmit the acceleration signalsrepresenting the opposite polarity to the control unit 712. Furtherdetailed information on the tangential acceleration data for use withthe remote tire monitor system is found in U.S. Pat. No. 6,204,758 toWacker et al., which is in its entirety incorporated herein byreference.

FIG. 10 is a flowchart illustrating an operation of the remote tiremonitor system 702 for determining left and right position informationusing the polarity of the acceleration. One of the tire monitors 724˜730transmits tire information signals received by the front detector 714and the control unit 712. The front detector 714 detects RF signals atblock 1002 and provides transmission indications to the control unit 712at block 1004. The control unit 712 receives RF signals at block 1006and demodulates the signals at block 1008. The control unit 712 extractsthe identifiers from the received signal at block 1014. At block 1010,the control unit 712 is provided with a vehicle moving directiondetected by using other sensors, gear mechanism or any other suitabledevices.

At block 1018, the control unit 712 selects two identifiers having thedetected modulations as transmission indications. As described above,the control unit 712 does not detect any modulation from the rear tiremonitors because the front detector 714 does not detect any RFtransmission. The control unit 712 assigns the two identifiers to thefront tires and remaining two identifiers to the rear tires at block1022. At block 1016, the control unit 712 operates to detect thepolarity of the tangential acceleration from the received RF signals. Atblock 1020, the control unit 712 retrieves left or right positioninformation corresponding to the polarity of the tangentialacceleration. The control unit 712 further takes into account thevehicle moving direction because the wheel rotation direction differs asthe vehicle moves forward or rearward. The polarity of the tangentialacceleration directly relates to the wheel rotation direction. At block1024, the control unit 712 determines front left and front rightpositions, and rear left and rear right positions. The identifiers arestored with the location information at block 1026.

In another embodiment, the acceleration sensor detects relationship oftwo types of acceleration and generates a resulting signal. Theacceleration sensor may be a dual-axis sensor and detect the centrifugalacceleration and the tangential acceleration along two orthogonal axes.Depending on the rotation direction of the wheels, i.e., clockwise orcounterclockwise, a signal for the centrifugal acceleration and a signalfor the tangential acceleration may develop phase difference. For thispurpose, the acceleration sensor may generate the resulting signal in asine wave form. The sine wave output signal may describe accelerationdue to gravity plus centrifugal or tangential acceleration components.As noted above, the tires on the left side and the right side rotate inthe opposite directions. For example, the tires on the left side rotatein a clockwise direction, whereas the tires on the right side rotate ina counterclockwise direction. Depending on the direction of the rotationof the wheel, two sine waveforms produced by the acceleration sensorsare out of phase and one axis will lead or lag the other axis. Forexample, if a tire on the left side rotates in a counterclockwisedirection, acceleration along the z axis may lead acceleration along thex axis by 90 degrees. Conversely, a tire on the right side rotates in aclockwise direction and acceleration along the z axis may lagacceleration along the x axis by 90 degrees. Further detaileddescription on the acceleration sensor and the lead/lag information isfound in the copending application Ser. No. 10/125,043, which isincorporated herein by reference in its entirety.

This lead/lag relationship, combined with the rotation direction,enables the control unit 712 to determine left versus right positioninformation. The operation of the remote tire monitor system 702 issubstantially similar to the operation described in connection with FIG.10. The control unit 712 receives the detected modulations astransmission indications from the RF detector 714 and receives RFsignals from the receiver. The control unit 712 associates theidentifiers with a number of detected modulations and determines frontversus rear position based on the number of detected modulations. Thecontrol unit 712 detects a vehicle moving direction and accelerationvalues representing phase difference of the tangential acceleration andthe centrifugal acceleration. The left and right position informationcorresponding to phase difference of two types of acceleration signalsmay be preprogrammed. Specifically, when the vehicle moves forward, theleft wheel rotates in a clockwise direction and the right wheel rotatesin a counter-clockwise direction. For the left wheel, acceleration alongthe z axis may lag acceleration along the x axis by 90 degrees, and forthe right wheel, acceleration along the z axis may lead accelerationalong the x axis by 90 degrees. The acceleration sensors detect thisphase difference from the left wheels and the right wheels and transmitit to the control unit 712. Based on the vehicle moving direction, thecontrol unit 714 is able to determine the rotation direction of the leftwheels and the right wheels. Then, the control unit 712 associates theleft and right position with the acceleration signal representing theacceleration values. As a result, an auto-location of four corners ofthe vehicle is completed.

The remote tire monitor system 702 and its operations are describedabove, but various other systems are possible. Instead of the front RFdetector 714, a rear RF detector, a left RF detector or a right RFdetector may be used. The rear RF detector may be positioned to beproximate a rear axle.

The left or right RF detector may be positioned to be proximate left andright sides of the vehicle, respectively. For instance, a remote tiremonitor system having a right RF detector for use with a four-wheelvehicle operates as follows. The right RF detector may be positionedproximate rear tire monitors, in particular, a rear right tire monitor.The control unit may first determine left and right position informationby comparing counter values of four identifiers. Two identifiers withhigher counter values than the other two may be assigned to right tiremonitors. The other two identifiers may be assigned to left tiremonitors. In addition, because the right RF detector is positionedproximate a rear axle, the control unit may determine front versus rearposition information. Between the two identifiers assigned to the righttire monitors, the identifier with a higher counter value may beassociated with the rear right tire monitor. The other identifier isassociated with the rear left tire monitor. In the same way, the othertwo identifiers may be associated with the left front and left rear tiremonitors.

In other embodiment, the right RF detector is positioned off-center,i.e., proximate the right side of the vehicle and midway between thefront axle and the rear axle. As noted above, the control unit is ableto determine right versus left position information with the detectedtransmissions indications. Other method of determining front versus rearposition information is needed because the RF detector is not proximateboth the front axle and the rear axle. The RSSI signal or accelerationsignals described above may be used to determine the front versus rearposition.

From the foregoing, it can be seen that the embodiments present a methodand apparatus which automatically conveys wheel position and data to areceiver in a vehicle. The remote tire monitor system employs a singleRF detector to generate a transmission indication upon detection of eachRF transmission from the tire monitors. With the single RF detector, thesystem control unit may determine position information such as frontversus rear and/or left versus right. The system control unit may usethe signal strength of the transmission to determine the remainder ofthe position information after determining front versus rear or leftversus right. Further, the system control unit may use the signalstrength of the transmission to determine the entire positioninformation. This feature is particularly suitable if the RF detectordoes not properly operate. Even after changes in tire position due totire rotation or replacement of a tire, the system automaticallyre-learns the position of the tires on the vehicle.

A single, inexpensive RF detector is needed to identify position of tiremonitors associated with each tire. The single RF detector operates todetermine position information, regardless of size and type of avehicle. The use of the RF receiver in addition to the RF detectorfurther improves accuracy and efficiency of system operation. Uponmalfunction of the RF detector, the RF receiver including the RSSIcircuit may serve as a supplemental means to determine positioninformation.

It is therefore intended that the foregoing detailed description beregarded as illustrative rather than limiting, and that it be understoodthat it is the following claims, including all equivalents, that areintended to define the spirit and scope of this invention.

1. A remote tire monitor system, comprising: a plurality of tiremonitors associated with wheels of a vehicle and operable to transmittire information; a single radio frequency (RF) detector operable todetect a RF transmission from two or more tire monitors and produce adetected transmission indication; a receiver operable to receive thetire information; and a control unit coupled with the RF detector andthe receiver, the control unit operable to determine positions of theplurality of tire monitors based on the detected transmission indicationand the received tire information.
 2. The remote tire system of claim 1,wherein the control unit is operable to count the detected transmissionindication and associate the plurality of tire monitors with frontversus rear position based on a count value.
 3. The remote tire systemof claim 1, wherein the control unit is operable to count the detectedtransmission indication and associate the plurality of tire monitorswith left versus right position based on the count value.
 4. The remotetire system of claim 2, wherein the control unit is operable to comparecount values of the received detected transmission indication for theplurality of tire monitors and determine left versus right position forthe plurality of tire monitors associated with the front versus rearposition.
 5. The remote tire monitor system of claim 4, wherein thecontrol unit is operable to store a distance between the detector andeach tire monitor and associate the distance information with the countvalues.
 6. The remote tire monitor system of claim 1, wherein thedetector is positioned off-center and proximate either a front axle or arear axle.
 7. A remote tire monitor system for use with a vehicle havinga front side, a rear side, a left side and a right side, comprising: aplurality of tire monitors associated with each side of the vehicle andoperable to transmit tire information; a single radio frequency (RF)detector positioned proximate one side of the vehicle and generate atransmission indication in response to radio frequency (RF)transmissions from at least one of the plurality of tire monitors; areceiver operable to receive the tire information; and a control unitcoupled with the RF detector and the receiver, the control unit operableto determine positions of the plurality of tire monitors based on thetransmission indication and the tire information.
 8. The remote tiremonitor system of claim 7, wherein the detector is positioned proximateeither the front side or the rear side and operable to detect RFtransmissions from tire monitors proximate the detector.
 9. The remotetire monitor system of claim 7, wherein the detector is positionedproximate either the left side or the right side and operable to detectRF transmissions from tire monitors proximate the detector.
 10. Theremote tire monitor system of claim 8, wherein the control unit isoperable to evaluate a received signal strength for each transmissionfrom the plurality of tire monitors.
 11. The remote tire monitor systemof claim 10, wherein the control unit is operable to determine frontversus rear position information based on the detected transmissionindication and left versus right position information based on thereceived signal strength.
 12. The remote tire monitor system of claim10, wherein the control unit is configured to detect a malfunctioning ofthe detector and determine front versus rear position information andleft versus right position information based on the received signalstrength upon detection of the malfunctioning.
 13. The remote tiremonitor system of claim 8, wherein each tire monitor includes anacceleration sensor to detect acceleration values and generate anacceleration signal for the acceleration values and the control unit isoperable to evaluate the acceleration signal for each transmission fromthe plurality of tire monitors.
 14. The remote tire system of claim 13,wherein the control unit is operable to determine front versus rearposition information based on the transmission indication and leftversus right position information based on a polarity of theacceleration signal.
 15. The remote tire system of claim 13, wherein thecontrol unit is operable to determine front versus rear positioninformation based on the transmission indication and left versus rightposition information based on lead/lag relationship of the accelerationsignal.
 16. A tire monitor method for use with a vehicle having a frontside, a rear side, a left side and a right side, the method comprising:positioning a single radio frequency (RF) detector proximate one side ofthe vehicle; at the single RF detector, detecting RF transmissions fromat least one of a plurality of tire monitors associated with each sideof the vehicle; at a receiver, receiving tire data from the plurality oftire monitors; and at a control unit, determining positions of theplurality of tire monitors based on the detected RF transmissions andthe tire data.
 17. The tire monitor method of claim 16, furthercomprising: at the control unit, counting a number of detectedtransmissions from each tire monitor; processing the received tire datato extract an identifier of each tire monitor; and associating theidentifier with the number of detected transmission.
 18. The tiremonitor method of claim 17, further comprising: at the control unit,comparing the number of detected transmissions among the plurality oftire monitors; and selecting at least one identifier having a greaternumber of the detected transmissions than the rest of the tire monitors.19. The tire monitor method of claim 18, further comprising: assigningthe selected identifier to at least one tire monitor proximate thesingle RF detector; and assigning the remaining identifiers to at leastone tire monitor distal from the signal RF detector.
 20. The tiremonitor method of claim 16, wherein detecting transmissions comprises:detecting the transmissions from tire monitors proximate the single RFdetector; and detecting no transmissions from tire monitors distal fromthe single RF detector.
 21. The tire monitor method of claim 20, furthercomprising: selecting a first identifier associated with the detectedtransmissions; selecting a second identifier associated with notransmissions; assigning the first identifier to the tire monitorsproximate the RF detector and assigning the second identifier to thetire monitors distal from the RF detector.
 22. The tire monitor methodof claim 21, further comprising: at the control unit, determining areceived signal strength from each tire monitor; determining a leftversus right position of the tire monitors proximate the front sidebased on the received signal strength; and determining the left versusright position of the tire monitors proximate the rear side based on thereceived signal strength.
 23. The tire monitor method of claim 21,further comprising: at the control unit, determining a received signalstrength from each tire monitor; determining a front versus rearposition of the tire monitors proximate the left side based on thereceived signal strength; and determining the front versus rear positionof the tire monitors proximate the right side based on the receivedsignal strength.
 24. The tire monitor method of claim 21, furthercomprising: at the tire monitors, generating acceleration signalsrepresenting acceleration values that arise from rotation of wheels; atthe control unit, evaluating a polarity of the acceleration signals; anddetermining a left versus right position of the tire monitors based onthe polarity of the acceleration.
 25. The tire monitor method of claim21, further comprising: at the tire monitors, generating accelerationsignals representing acceleration values that arise from rotation ofwheels; at the control unit, evaluating a polarity of the accelerationsignals; and determining a front versus rear position of the tiremonitors based on the polarity of the acceleration.
 26. The tire monitormethod of claim 21, further comprising: at the tire monitors, generatingacceleration signals representing acceleration values that arise fromrotation of wheels; at the control unit, evaluating lead/lagrelationship of the acceleration signals; and determining a left versusright position of the tire monitors based on the lead/lag relationshipof the acceleration.
 27. The tire monitor method of claim 21, furthercomprising: at the tire monitors, generating acceleration signalsrepresenting acceleration values that arise from rotation of wheels; atthe control unit, evaluating lead/lag relationship of the accelerationsignals; and determining a front versus rear position of the tiremonitors based on the lead/lag relationship of the acceleration.
 28. Thetire monitor method of claim 16, further comprising: positioning thesingle detector to be off-center and proximate one of the front axle andthe rear axle.
 29. The tire monitor method of claim 28, furthercomprising: at the control unit, comparing the number of detectedtransmissions among the plurality of tire monitors; assigning theidentifier having the greatest number of detected transmissions to atire monitor proximate the single RF detector; and assigning theidentifier having the smallest number of detected transmissions to atire monitor distal from the signal RF detector.